The invention relates to electrical supply control systems for motor vehicles and is concerned particularly with safeguarding an electrical storage battery in a motor vehicle from excessive discharge.
There is an increasing tendency to equip motor vehicles with electrically operated facilities which take power from the vehicle battery with the vehicle unattended. Typical examples are memories for preferred positions of electrically adjustable devices such as seats and mirrors and memories for radio tuning. Another example is the vehicle clock. In addition to these facilities which can not normally be isolated from the electrical supply under the control of a driver, other electrical facilities may be left on accidentally when a vehicle is unattended or may fail to a condition where they draw current inadvertently. All these factors tend to cause the battery to run down when the vehicle is left for a long period.
The problem of inadvertent battery discharge is particularly significant with a new vehicle which may remain unused for a few weeks or even months during transit from manufacturing facility to dealership or in storage awaiting a customer. Allowing the battery to discharge in these conditions not only results in the embarrassment of a flat battery but can do permanent damage to the battery.
Disconnection of the vehicle battery during storage can be an effective contribution to solving this problem. However, electrical power may be required within the vehicle at short notice, for example to start the engine for vehicle manoeuvring during transit or when rearranging vehicles in storage. For this reason simple disconnection of battery terminals is impractical. It has also been proposed to provide a relay in the battery circuit of the vehicle and to connect it into the vehicle electrical system in such a way that power is normally isolated from ignition and other load circuits when the normal ignition switch is off but the relay is energised on switching on the ignition to provide power to both the ignition and the other loads. This relay is discarded prior to delivery of the vehicle to a customer so that those facilities such as memories referred to above which are required continuously are provided with power even when the ignition is off. Provision of a relay for such temporary use and the requirement for its removal render this arrangement relatively uneconomic.
It has also been proposed to provide a motor vehicle with an isolation switch which disconnects the battery from the electrical facilities of the car. Such a switch provides a security function if the switch is not readily accessible. It also can be used to guard against inadvertent battery discharge when the vehicle is left unattended for several days. It can also be useful during vehicle servicing when there is often a requirement to disconnect the battery. Switches for this purpose have to be particularly heavy duty because they pass large currents and have to remain reliable for a long period of time. For example, a switch could remain closed for some years and then need to operate perfectly the first time that it is opened and reclosed.
An object of the invention is to provide an electrical supply control system for a motor vehicle in which a wide range of control possibilities are available with a single switch.